hAtom rel=bookmark backcompat only for classic roots

[gRegorLove]

rel=bookmark should only be parsed as u-url in a classic root microformat. I discovered via snarfed/bridgy#758 (comment) that it's always parsing as u-url, even inside mf2 roots.

Sample HTML:

<div class="h-entry">
<p> <a href="/article" rel="bookmark" class="p-name">Title of Post</a> </p>
<div class="e-content"><p> This is the post </p> </div>
</div>

mf2py parse (correct):

{
 "items": [
  {
   "type": [
    "h-entry"
   ], 
   "properties": {
    "name": [
     "Title of Post"
    ], 
    "content": [
     {
      "value": " This is the post  ", 
      "html": "<p> This is the post </p> "
     }
    ]
   }
  }
 ], 
 "rels": {
  "bookmark": [
   "/article"
  ]
 }, 
 "rel-urls": {
  "/article": {
   "text": "Title of Post", 
   "rels": [
    "bookmark"
   ]
  }
 }
}

php-mf2 parse (incorrect)

{
    "items": [
        {
            "type": [
                "h-entry"
            ],
            "properties": {
                "name": [
                    "Title of Post"
                ],
                "url": [
                    "/article"
                ],
                "content": [
                    {
                        "html": "<p> This is the post </p> ",
                        "value": "This is the post"
                    }
                ]
            }
        }
    ],
    "rels": {
        "bookmark": [
            "/article"
        ]
    },
    "debug": {
        "package": "https://packagist.org/packages/mf2/mf2",
        "version": "v0.3.2",
        "note": [
            "This output was generated from the php-mf2 library available at https://github.com/indieweb/php-mf2",
            "Please file any issues with the parser at https://github.com/indieweb/php-mf2/issues"
        ]
    }
}